When a vehicle accelerates strongly it is possible to observe that motor vehicles with a driven front axle influences the steering as a result of the drive forces. The driver of the vehicle must actively intervene in order to counteract the steering force error which is generated, and to maintain the selected course. Some causes for this include secondary torques from the external constant velocity joints of the drive shafts if there are different bending angles on both sides of the vehicle; asymmetrical drive forces resulting from the friction in the differential gear mechanism; or a differential gear mechanism which is self locking or locks in a controlled fashion or from forces of inertia. Furthermore, strong influences come from the geometric conditions of the driven front wheels with respect to the road surface, as a result of which the force application point of the tire force moves.
It is known to use a bearing block in the longer half shaft in order to bring about an equal length of the left and right hand half shafts. This bearing block is however extremely costly to acquire and mount and applies an additional weight to the motor vehicle so that, for example, the fuel consumption increases. It is also known to reduce the friction of a differential bevel gear mechanism. However, this requires a high degree of technical complexity and is therefore possible only to a limited extent. In many motor vehicles this friction is even desired as a locking effect in order to increase the acceleration capability of the vehicle. Furthermore it is known that a short lever arm of the tire force is advantageous for the virtual steering axis of the wheel. However, for structural reasons, it is often not possible to shorten this lever arm.
Both hydraulic power steering systems and manual power steering systems of the known type can only be changed in terms of their steering property or their settings (tuning) under extremely large and costly circumstances in order to reduce the abovementioned disadvantages. However, these changes are generally always accompanied by the worsening of other desired properties. In contrast, the electric power steering system (EPAS) uses a microprocessor and therefore can reach a specific “smart” operating level. This “smart” operating level makes it possible to adapt the steering properties of the motor vehicle to the requirements and operating conditions of the vehicle, the desires of the driver, or to actively counteract the disturbances.
A fundamental problem in the configuration of motor vehicles related to the vehicle's handling properties, are steering torques or disturbance variables which can be perceived by the driver of the vehicle. In this context, the designer of the motor vehicle has a number of alternative approaches available, but all the currently known options are also subject to disadvantages. Electronically controlled steering systems (EPAS) are presently being used to an ever greater extent in the automobile industry. As a result, it now makes it possible to obtain previously unforeseen advantages as the motor vehicle industry is increasingly applying microprocessor technology in steering systems (EPAS).
Drive train influences or drive influences, in particular on a steerable axle of the motor vehicle, could possibly have an adverse effect on a steering sensation of the driver of the vehicle such that the driver of the motor vehicle could find it to be an unacceptable nuisance during normal control of the motor vehicle. In particular for front wheel drive but also for all wheel drive vehicles, the steering sensation is largely influenced by the drive forces of the engine. These influences are a function of the system design and their intensity depends to a great extent on the front axle design, external influences, and the performance capability of the drive train. Because these perceived changes in the steering torque do not correspond to the natural feedback of the vehicle to a specific situation and are therefore perceived by the driver as a disturbance. In extreme cases, the influences may be so strong that they cause a change in direction of the vehicle, which can lead to considerable damage, even to personal injury.